In a lamination molding method using laser beam, a molding table capable of vertical movement is arranged in a chamber filled with inert gas. Then, a very thin material powder layer is formed on the molding table. Next, predetermined portions of this material powder layer are irradiated with the laser beam to sinter the material powder at the position of irradiation, thereby forming a sintered layer. These procedures are repeated to form a desired three-dimensional shape composed of a sintered body integrally formed by laminating a plurality of sintered layers. This lamination molding method is realized by a lamination molding apparatus. These days, it is required to enlarge such a lamination molding apparatus so that a larger molded object can be formed.
In the conventional lamination molding apparatus disclosed in Patent Literature 1, the galvanometer scanner is disposed on the upper plate of the chamber right above the center of the molding table. A condensing lens is provided between the galvanometer scanner and the laser source, and a window is provided between the galvanometer scanner and the molding table. The galvanometer scanner has a pair of (two-axis) galvanometer mirrors and is configured to scan laser beams on the X and Y axes. If there is no interference with the frame of the window, there is no physical restriction in the irradiation region of the laser beam. However, as the irradiation angle of the laser beam with respect to the vertical axis increases, as the deformation of the shape of the irradiation spot increases, or as the irradiation energy varies, the accuracy of sintering the material powder uniformly decreases. Further, if the galvanometer scanner is disposed at a high position, the irradiation region with the laser beam can be expanded. However, the laser beam irradiated with a long irradiation distance at a large irradiation angle largely changes the position of irradiation spot with a slight change in the attachment position of the galvanometer scanner due to thermal deformation of the chamber. Actually, there is a problem that the maximum irradiation range is limited to a certain extent.
Further, the conventional lamination molding apparatus mainly supplies or discharges inert gas from the side wall and the top plate of the chamber, and removes fumes generated when the material powder is sintered by irradiation of the laser beam. Achieving the above object of enlarging the irradiation range, the distance between the irradiation spot and the inert gas supplying opening or the fume discharging opening becomes larger in the conventional lamination molding apparatus. Then, fume removal cannot be completed in time, when the laser beam is scanned with the scan speed and the irradiation energy calculated from the current standard molding time. As a result, it is impossible to maintain a clean environment to the extent that molding in the chamber is possible, which may hinder molding. In order to perform proper molding, it is necessary to slow down the scan speed sufficiently, to reduce the irradiation energy, and to remove fumes while intermittently providing a pause time in which the laser beam is not irradiated, so that a suitable environment is maintained. However, since the molding region becomes larger, the efficiency in molding is considerably lower, and there is a concern that the molding time becomes unacceptably long.